When required to drill in marshes and mud flats, one practice for many years has been to dredge canals to drill sites so the drilling equipment could be floated to location on a barge. Such dredging often causes ecological damage, destroying estuaries and other natural habitats. Another practice used to move land rigs to a drill site is to build roads by laying timber which is extremely expensive and causes waste of a great many trees as well as the residual damage to the countryside, the natural slopes, drain fields and such. Obviously, delays and costs become excessive and logistics become tedious. Various types of "swamp buggies" and such devices have been successfully used to transport personnel and light equipment but to transport large heavy loads such as a drill barge over marshland, water and dry land, it is necessary to establish a common interface such as an air cushion between the vehicles and the earth's surface so as to reduce friction, bow resistance and stern drag to a minimum and to reduce environmental damage. Thus, the cost, power and weight required to propel a vehicle riding on an air cushion as known, and is at a minimum.
U.S. Pat. No. 3,183,988, depicts the use of many relatively small ground effect vehicles spaced contiguously around the periphery of the much larger unit to be transported. U.S. Pat. No. 3,840,089, depicts a similar arrangement but with means to maintain all units in rigid assembly.
However, no provision is made for firm and continuous position control. Should a surface effect vehicle carrying a heavy load, like a drilling rig and other necessary drilling equipment, travel along a surface having a slight slope sidewise, undesirable side movement would occur, causing the vehicle to go off course and perhaps to crash into trees or such. Also, when positioning with respect to an existing wellhead for workover operations, no moving off from a completed well, crashing into the wellhead is likely to occur due to the highly unstable position control of a conventional surface effect vehicle. Even a gust of wind can cause a sudden and unexpected movement of a conventional surface effect vehicle.
The use of numerous small surface effect vehicles to transport a drilling barge to marshland wellsites is not desirable due to the remote locations of such sites. Substantial manpower requirements to attach and detach such multiple units under remote marshland conditions, and to return them to some storage location would make their use to move drill rigs questionable at best. Since drill rigs are usually on a site for long periods of time, to leave the small vehicles attached would not be economically feasible and would subject them to severe damage during normal drilling and handling operations.
Mounted on a typical drilling barge are items of great weight, such as the derrick, substructure, mud pumps, generators, mud system tanks and draw works which cause the average total weight per square foot of bearing load of the barge hull to be greater than an air cushion under the barge hull alone can support. Prior art noted above indicates that the barge hull must be made big enough to gain more area and therefore sufficient lifting capacity for transport, although the excess area is not required for the drilling operation.
During the drilling of a deep well, many unpredictable circumstances occur, requiring the storage of large amounts of pipe, fuel, mud, fresh water, salt water chemicals and such, at any given time. Accordingly, when the rig is to be moved off location, whatever materials are on board, must be moved with the rig to the next drillsite especially since environmental considerations prevent dumping and since transport costs over marshland discourage temporary storage at some distant location while the rig is being moved to the new drillsite. Therefore, considerable quantities of pipe and liquids must be moved on a surface effect vehicle which requires a load distribution far more precise than is required aboard a ship. Accordingly, there is need for a system to adjust the combined effect of fixed loads, solid variable loads and fluid variable loads so as not to cause the surface effect vehicles to list or dip excessively.